DAS measures dynamic axial strain or strain rate transferred into the sensing fiber. It is often described as a distributed microphone, but the usable signal depends on how the cable is constructed, installed and coupled to the monitored asset or ground.
How a vibration becomes a signal — phase-OTDR
The interrogator launches coherent light into the fiber and analyses phase changes in Rayleigh backscatter. A disturbance transferred into the cable produces dynamic axial strain. The system resolves it in spatial channels defined by the selected gauge length, sampling and processing configuration; waveform bandwidth and localisation are mode-dependent.
Reading the data: the waterfall plot
Because DAS measures successive spatial channels along the route, it can return thousands of data channels at once. They are plotted as a waterfall plot: distance along the cable runs horizontally, time runs vertically, and colour is vibration strength. Every event leaves a different signature — and that is what separates digging from a passing car or a person walking by. Pick a source:
Illustrative model — speeds and amplitudes chosen for legibility. In a real system the slope of a trace corresponds to the speed of the source, and brightness to vibration energy.
Where DAS creates operational value
Pipelines
Early warning of third-party interference and leak-associated signatures can help operators investigate the relevant route section sooner.*
Perimeter security
Continuous fence or buried-boundary monitoring with configured event detectors; route tuning can reduce nuisance alerts from benign activity.*
Rail corridors
Train and trackside activity monitoring where the available route-side fiber has suitable optical performance and mechanical coupling.
DAS at INTERLAB
INTERLAB supplies DAS platforms from the Luna Innovations sensing group, including OptaSense and Silixa:
* Manufacturer maxima refer to specific products, operating modes and channel counts; they are not necessarily available simultaneously. Coverage, spatial granularity, measurement rate and uncertainty are confirmed for the selected configuration and application conditions.
For system sizing, provide the route length, number and condition of fibers, cable construction, events to detect, required localisation and background activity. Existing dark fiber should be qualified and normally piloted.
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Frequently asked questions
Can DAS distinguish an excavator from someone walking?
Can existing dark fiber be used for DAS?
What range does one DAS interrogator cover?
What information is needed to size a DAS system?
Need a DAS configuration for a real route?
Send the route length, available fibers, cable construction, events to detect and required localisation. We will compare suitable OptaSense and Silixa configurations and identify whether route qualification or a pilot is needed.
Request a DAS configuration →